Control and protection of electrical apparatus



Oct. 12,1926. 1,602,993

H. TINSLEY ET AL CONTROL AND PROTECTION OF ELECTRICAL AfiPAR-ATUS Filed April 1. 1926 Patented Oct. 12, 1926.

UNITED STATES PATENT OFFICE.

HORACE T INSLEY, OF WAKEFIELD, AND JOHN HENRY COX, OF OUTVVOOD, NEAR WAKEFIELD, ENGLAND.

CONTROL AND PROTECTION OF ELECTRICAL APPARATUS.

Application filed April 1, 1926, Serial No. 99,162, and in Great Britain September 17, 1924.

This invention relates to the combined remote or distant control and the protection by ear-thing of electrical apparatus and more particularly portable apparatus such as electrically driven coal cutting machines and conveyors used in mines. In portable apparatus of this type, it has been usual to control the machines by means of electrical gear comprising a main switch hand-operated in the gate, a trailing cable having four cores and a starting switch in the body of the machine. In such an arrangement, however, it is possible to make the cable alive by means of the main switch whether or not the plug of the trailing cable is. exposed, and the starting-switch on the machine controls the main line voltage with danger of accident in case of faulty insulation.

According to this invention the main control mechanism for supplying line current to the distant machine 15 operated from the distant machine by means of the auxiliary or pilot circuit which employs low voltage currentdistinct from the main current supplied at the usual line voltage. The earth conductor is utilized as the return for the low voltage pilot or controlling current so that no part of the main circuit can be exposed to line voltage unless the earth circuit is first completed. It is to be understood that the invention relates specifically to the combined earthing and distant control of the main circuit, that is, the closing of the circuit for starting purposes by operating the control switch at the machine which controls the main switch at the gate end.

In order that the said invention may be clearly understood and readily carried into effect the same will now be described more fully with reference to the accompanying drawing, which is a circuit diagram of apparatus embodying this invention and suitable for use in connection with an electrically driven coal cutting machine or other electrical machine of analogous type in which the apparatus is under remote control. The gate or remote control end of the apparatus is indicated at the left of the figure and the motor end at the ri ht.

A is a flexible tralling cable connected up between the gate and switch B and the machine. This cable has an internal conductor or a metallic sheathing a forming an earth connection between the gate end switch B and the machine when the ends of the cable are connected up. The cable in addition to carrying the usual line conductors C is provided with a pilot conductor D, terminating, as in the case of the line conductors, in con tacts in plug or other connections d, d at the ends adapted to connect up with coupling members on the machine and at the gate end switch B, the pilot conductor contact d on the machine being connected to a control switch E and earthed through the machine frame F. A high resistance lamp 6 may be placed across the terminals of the control switch to indicate current in this circuit. The line conductors 0, shown as the three conductors of a three phase circuit, have plug or like connections a, c at their ends.

The pilot conductor terminal d at the gate end switch B is connected to the frame G through a solenoid b controlling the opera tion of the switch B through the secondary winding of the step-down transformer H. The solenoid 1) forms the only means of closing the gate end switch B and can be energized only through the pilot circuit D, the control switch E on the machine and the earth. The solenoid is (lo-energized immediately when this pilot circuit becomes im paired or broken, whereupon the main circuit is immediately opened at the switch B. The primary of the transformer H belonging to the pilot circuit is controlled by means of a double pole switch J by which the machine and trailing cable A can be completely isolated when the switch is opened.

The three conductors C are connected through the three contact members 6 of the main switch B with the three leads 6 when the members 6 are in closed position, the leads 6 leading from a source of three phase current. The conductors C, when the gate end and the machine are connected up at a, 0, lead to the motor indicated by the three phase mesh windings M. The motor circuit is closed by the control switch E on starting the machine, the control switch including a reversing switch 6' which connects two of the main conductors C to the required points of the motor windings M, the third point of the mesh at m being connected directly to the third conductor C (the uppermost conductors C in the diagram). The reversing switch is of well known type and connects up the contacts m belonging IOU lll

, against a short circuit, with the to the win-dings I i to the contacts 6 belonging to the conductors C according to the desired direction of rotation of the motor, as is well understood. The control switch also includes the pilot switch 6 which when closed connects up the contacts (Z of the pilot and earthing circuit, short ci'rcuiting the lamp 6 which serves only to indicate the existance of a potential when the machine is not running. The pilot and reversing switches e and e are, of course, operable separately, but arranged so that the reversing switch is moved only when the pilot switch is in open position.

The switch closing solenoid Z; is suitably designed to require a current of predetermined strength to energize it ell ectively and maintain the s itch B in closed position so that any reduction in the current below the predetermined level will immediately open the main switch. The current in the transformer coupled pilot circuit is proportionate to the line voltage, so that any material din inution in that voltage at once causes the opening of the main switch.

To prevent risk of any conductor being made aliye while exposed or exposed while still aliye the plug and socket connections of the pilot wire at the ends of the cable between the machine on the one hand and the gate end switch on the other hand are arranged to make contact only when the plugs are fully home and to break contact imme diately a plug is partly withdrawn. Thus on the withdrawal or partial withdrawal of a plug the pilot circuit is immediately broken and the gate end switch B tripped, breaking the line circuit and preventing any plug contacts being exposed while still alive.

The pilot circuit may itself be protected resulting danger of setting the machinery in motion, by means of the small solenoid or other trip coil (Z which may be inserted in the pilot circuit and arranged to operate the double pole switch J (or other circuit breaking switch) should the current in the pilot circuit exceed a predetermined level.

The line conductors G are provided at the switch end with balanced overload coils c and are shown connected up at the motor end in mesh formation. The switch E as shown is an interlock-ed pilot switch and reversing switch. The general arrangement of the crcuits is known and does not require detailed description.

lVhat we claim and desire to secure by Letters Patent of the United States is 2-- 1. A control system for electrical machines situated at a distance from the control mechanism for the line current supply, comprising a main circuit, a source of supply of current for said main circuit, a pilot circuit, a source of supply of current for said pilot circuit, a switch at the gate end of the main line circuit, means in the pilot circuit for operating the said switch, means in the pilot circuit for cutting off the supply of current in the pilot circuit when an overload in the pilot circuit occurs, an electric machine at the other end of the main circuit and means situated at the machine for closing the said pilot circuit, whereby the means for operating the switch in the main line at the gate end is controlled.

2. A control system for electrical mach'aea situated at a distance from the control mechanism for the line current supply, comprising a main circuit, a source of supply of current for said main circuit, a tap-oil from said source of current supply, a transformer connected through a switch to said tap-o l'. a pilot circuit connected to the secondary winding of the transformer, a switch at the gate end of the main circuit, a solenoid in said pilot circuit for operating said switch in the main circuit, one side or said pilot circuit being grounded at said gate end, an electric machine at the other end of the main circuit, a switch adjacent said electric ma chine for controlling said pilot circuit. one side of said last mentioned switch being grounded and means in said pilot circuit a51- opening the switch between the transformer and the tap-off when an overload in the circuit occurs.

pilot HORACE TINSLEY. JOHN HENRY COX. 

